The present invention relates to co-pending U.S. patent application Ser. No. 652,386, filed Sept. 20, 1984, now U.S. Pat. No. 4,616,649, directed to a lancet assembly which is hereby incorporated by reference in its entirety, and also to such an assembly which provides automatic retractable lancet movement utilizing resilient means incorporated into the assembly having the dual function of damping the lancet drive movement, together with providing the automatic retraction of the lancet once the puncture is made.
Sharp-pointed lancets have been employed for many years to make a quick puncture or penetration of a patient's skin in order to provide a small outflow of blood. Various tests may be employed with only a small amount of blood so that the blood flowing from a finger prick is normally sufficient to carry out a substantial number of tests. However, due to the sensitive nerve endings in the fingertip area, this procedure sometimes induces a significant amount of pain in the patient, even though the skin puncture produces minimal cutting. Moreover, as will be understood, many people are frightened by the appearance of a blade or skin puncturing apparatus of any kind wherein the cutting portion is available for them to see prior to the puncture. In order to minimize potential pain, as well as reduce apprehension in a patient, it is desirable to make the thrust of the lancet through the patient's skin rapidly and to provide a rapid withdrawal and shielding of the lancet.
Other problems involved with such procedures include contamination by the technician in the procedures involved in taking the blood sample. That is, the patient may have some disease, and if the lancet blade which has carried out the puncture action should prick the skin of a technician subsequent to the initial puncture, the technician and/or nurse and/or doctor involved may be exposed to contamination. Thus, it is important to have automatic retraction of the blade immediately after puncture so that the blade is not exposed for an accidental puncture of someone else's skin.
Spring-loaded lancets of different types and forms have been well known and are typified, for example, by U.S. Pat. Nos. 55,620; 1,135,465; 3,030,959; 4,139,011; 4,203,446; 4,230,118; 4,449,529 and 4,388,925.
U.S. Pat. No. 4,203,446, noted above, is significant in that it teaches the puncture of the skin of a patient with a lancet which is retracted back into the device after piercing the patient's skin. In the patented device, the downward motion of the lancet is initiated by impact of a spring-loaded hammer, and as this motion continues the spring potential decreases. At the time of the impact, the return spring begins to compress and increase potential energy. When the potential energy in the return spring under compression exceeds the potential energy in the driving spring, compression of the return spring ends and decompression begins. This, then reverses the motion of the lancet.
However, impact is necessary to compress the return spring and increase its potential energy rapidly. Without the impact force, the spring forces would approach equilibrium and then there would be no reverse motion in order to retract the lancet out of the patient's skin. Moreover, since spring potential is critical in this patented device, a conical spring is relied upon to overcome recoil due to the surge of the larger return spring. Other problems include, of course, the cost of such an involved assembly. Despite the foregoing inventions, improvements in this field of lancets are still being sought.
With the invention described in co-pending application Ser. No. 652,386, an improved automatic retractable lancet assembly is provided which is relatively simple of construction and easily moldable into two pieces of plastic material. Nevertheless, this simple construction provides, through the utilization of two annular abutments on a lancet holder body assembly cooperating with a single annular integral abutment on a lance holder guide, a snap action drive for the lancet to rapidly drive the lancet for the puncture action, with an automatic retraction of the lancet once the puncture has been completed. Moreover, integral with the lance holder body assembly are springs which first provide a damping of the lancet drive, once the cooperating abutments provide the snap action, and, secondly, provide automatic retraction of the lancet. The lance holder portion of the assembly includes a skin compacting front end edge surrounding the lancet blade which automatically engages the skin around the puncture site and moves the skin to provide an accurate skin positioning area at the puncture site, so that the lancet makes a clean puncture rapidly in the area desired.
An improvement is provided with this invention in that an additional spring is incorporated into one of the two pieces forming the device. That is, positioned between the top "push-button" of the lance holder body and the lance is an additional spring which enhances the spring movements of the device described in the above-noted co-pending application. The additional spring not only increases the damping of the snap-action drive of the assembly, but also improves the rapidity with which the lancet is withdrawn, once puncture has been made. Moreover, this additional spring forms part of and is simultaneously molded during the formation of the lance holder body of the assembly of this invention.
The additional spring forming part of the single molded lance holder body is S-shaped in a form similar to that described in U.S. Pat. No. 4,449,529. As such the spring is maintained in a relaxed condition before and after use, with a momentarily extended condition during the snap-action drive. Because of its position, the spring has the effect of damping the thrust forward so as to reduce impact of the lancet body against the skin surface, and to enhance rapid withdrawal immediately upon piercing of the skin.
In accordance with principles of the present invention, the desired functions are achieved by virtue of a very simplified two-piece structure including a lance holder guide comprised of a simple elongated piece of semi-rigid material such as a plastic formed into an elongated body having substantially rectangular passage therethrough. Movable in the passage is an elongated lance holder assembly arranged to have an integral activation handle at one end thereof, and an arrangement for connection of a lance on the opposite end.
The lance holder body assembly, aside from the integral S-spring noted above, includes two spaced integral ridges around the perimeter thereof forming abutments, as well as integral resilient means in the form of leaf springs depending from the handle end of the lance holder body assembly. The abutments cooperate with a single integral abutment around the internal perimeter of the lance holder guide or housing for holding the two parts together prior to use, for providing the snap action in the drive of the lancet to provide the desired puncture, and for providing a stop in the return direction of movement of the lance holder. These two molded pieces together with the actual lancet blade provide an appropriate and accurate skin puncture for obtaining the desired quantity of blood for carrying out appropriate tests. Moreover, the arrangement is such that it may be immediately discarded without any danger of contamination by subsequent puncture of those who may handle the used lancet assembly. Nevertheless, even though the structure provides the several desired functions of a modern lancet in use, it is easily manufactured by conventional molding procedures.